In an attempt to characterize the structural organization of Abelson murine leukemia virus, we have cloned the integrated proviral DNA of A-MuLV from EcoRI digests of transformed mink cell genomic DNA in bacteriophage lambda gt WES lambda B. The proviral DNA containing phages were identified using Moloney MuLV cDNA and are being analyzed by restriction enzyme digestions, heteroduplex methods and infectivity.